The ignition process is essentially dependent on the type of heat flux, whether it is static or dynamic (when the ignition of fuels is initiated by time-dependent heat flux). At the same time, the ignition of fuels under dynamic conditions has been insufficiently studied.
In this work we analyzed the ignition of the wood samples subjected to the dynamic heat flux. The experimental setup was created on the base of the optical wave "Uran-1" with a radiation source. The intensity of the heat flux was changed during the experiment by moving the test sample along the optical axis of the elliptic reflector in the setup. Pine wood was used as the test samples.
When the radiation flux decreases, the delay time for ignition of the pine samples is 2-2.5 times less than that for the constant radiation flux. At the same time, the decrease in value of heat flux leads to the fact that the delay time of ignition increases faster under static conditions than under dynamic ones.
The analysis of the data shows that the ignition delay time for the increasing flux of radiant energy is smaller than for a constant flux. The difference in time is from 2 to 3 times. For the decreasing flux, a similar pattern is observed. However, the ignition delay time for the increasing flux of radiant energy decreases slower than for the decreasing flux with the increase in time.
The results obtained can be used to improve the prediction of dangerous zones for ignition of wood in wildland and anthropogenic fires.